Spectral type dependent rotational braking and strong magnetic flux in three components of the late-M multiple system LHS 1070

TL;DR

This study measures rotation and magnetic fields in the late-M star system LHS 1070, revealing spectral type-dependent braking and complex magnetic field effects in low-mass stars.

Contribution

It provides the first detailed magnetic and rotational analysis of all three components, highlighting differences linked to spectral type and magnetic topology.

Findings

Magnetic flux of several kilo-Gauss in all components.

Slower rotation in earlier M star compared to late-M components.

Magnetic flux varies independently of rotation rate in low-mass stars.

Abstract

We show individual high resolution spectra of components A, B, and C of the nearby late-M type multiple system LHS 1070. Component A is a mid-M star, B and C are known to have masses at the threshold to brown dwarfs. From our spectra we measure rotation velocities and the mean magnetic field for all three components individually. We find magnetic flux on the order of several kilo-Gauss in all components. The rotation velocities of the two late-M objects B and C are similar (vsini = 16km/s), the earlier A component is spinning only at about half that rate. This suggests weakening of net rotational braking at late-M spectral type, and that the lack of slowly rotating late-M and L dwarfs is real. Furthermore, we found that magnetic flux in the B component is about twice as strong as in component C at similar rotation rate. This indicates that rotational braking is not proportional to magnetic field strength in fully convective objects, and that a different field topology is the reason for the weak braking in low mass objects.